This study concerns an investigation of the role of Ca2+ in the regulation of GABA binding to GABA-A and GABA-B recognition sites located in the synaptic membranes of rat brain. At 37C the binding of 3H-GABA to GABA-B recognition sites is dramatically stimulated by Ca2+ with a Ka of about 10-5M while the binding to GABA-A recognition sites is only slightly but significantly enhanced by Ca2+ with a Ka of about 5x10-7M. The Ca2+ effect of GABA-A recognition sites is temperature dependent and requires calmodulin but involves neither phospholipase A2 nor Ca2+-dependent proteases. Only GABA-A recognition sites are linked to benzodiazepine recognition sites and also this interaction is modulated by Ca2+ at physiological ion concentrations. Diazepam and low MuM Ca2+ cause the appearance of a high affinity binding site for GABA-A recognition sites. The number of GABA-B recognition sites measured at 37C is about 70% higher than that measured at 4C. This temperature-dependent increase in the number of GABA-B recognition sites is calmodulin independent, probably Ca2+-dependent proteases are operative. We have also studied whether GABA-A and benzodiazepines recognition sites located on C6-glioma and neuroblastoma NB2a cells are linked to some other transducer, for instance phospholipase A2. In C6-glioma but not NB2a cells, prelabeled with 14C-arachidonic acid, GABA agonist muscimol stimulates the release of 14C-arachidonic acid. This increased release is due to an activation of phospholipase A2. This process is blocked by bicuculline, a classical GABA-A receptor blocker but not by inhibitors of Cl- channel or GABA uptake blockers. The phospholipase A2 activation by muscimol is potentiated by several benzodiazepines, but not by clonazepam. Analyses of the radioactive metabolites released by HPLC reveal that a substantial amount of prostaglandin D2 is formed when muscimol is supplemented with diazepam. Prostaglandin D2 may be a neuromodulator which serves as a linkage of glial cells to neuronal function. We are currently investigating the possibility of the involvement of glial benzodiazepine receptors in the regulation of GABA function mediated through the formation of certain classes of prostaglandins.